Natural gas consists primarily of methane (CH4), and includes smaller amounts of higher alkanes, CO2, N2, and H2S. It is used not only for heating and energy generation, but also as a chemical feedstock to produce commodity chemicals that can be then converted to plastics and specialty chemicals. Natural gas constitutes an enormous energy and chemical resource for the US where the recoverable amount is estimated to be 2,000 trillion ft3. Natural gas is however a poor transportation fuel because of its inherently low energy density. Technologies that can convert natural gas into liquid fuels at competitive prices will not only lessen our dependence on imported oil, but also eliminate the needs for retrofitting existing transportation infrastructure. Current chemical routes based on chemical conversion to syngas (CO & H2) through the Fischer-Tropsch process are not competitive for producing liquid fuels, as they suffer from both high capital costs and low conversion efficiencies. Bioconversion is a promising alternative because of its high specificity and high process energy efficiency all under very mild conditions. Thus, CH4 represents an ideal target for conversion to liquid fuels by biological processes or hybrid biological/catalytic processes.
Some progress has been made in the catalytic conversion of CH4 to methanol (MeOH), more biological means may be developed for converting methane to methanol, likely by a form of reverse methanogenesis. Non-naturally occurring or synthetic microbes expressing a heterologous methanol dehydrogenase (MDH) and other heterologous ribulose monophosphate (RuMP) pathway enzymes have been developed to grow in a medium comprising methanol (see WO 2015/108777 A1), but such heterologous MDH does not operate optimally under normal conditions (e.g., temperature) for microbes such as Escherichia coli (E. coli) strain commonly used to produce liquid fuel molecules or other commodity chemicals. There remains a need for non-naturally occurring methylotrophic microbes capable of converting methanol efficiently to liquid fuel molecules or other commodity chemicals.